The invention relates to a drill head insert or a drill head attachment and to a drill.
Drill head inserts and drill head attachments are typically used in drills to facilitate the feed of the drill in material which is difficult to machine, for instance concrete or rock. For this purpose, typical drill plates comprise cutting edges as drill head inserts which are configured between respective cutting faces and respective free faces. When viewed in the direction of rotation of the drill, the cutting face is in front of the cutting edge, whereas the free face is behind the cutting edge when viewed in direction of rotation of the drill. The cutting edge contributes to remove material to a substantial degree.
It is known that the drill properties of drill plates of this kind can be improved by providing the cutting edge, the adjacent cutting face and/or the adjacent free face with depressions. In this way, for instance, a profile of the contact pressure of the drill plate to the material can be optimized when axial pressure is applied and it can be ensured that good destruction forces can be achieved even if an impact drive synchronized with a rotary drive is used. Exemplary embodiments can be taken from the documents DE 297 23 948 U1, GB 2 201 910 A and DE 299 22 291 U1.
In drill plates of this type a crest line remains above a tip of the drill. The contact face (line contact) of the cutting edge is shortened in this manner, while the total length of cutting edges is increased at the same time. It has shown that this has a decelerating effect on the drilling progress which can also be referred to as drilling rate.
Tests have shown that the drilling progress is highly dependent on the tip of the drill. In the center of the tip of the drill no rotary movement (cutting speed) takes place. For this reason, the drilling progress is decelerated. If depressions are present, as is the case in drill plates which are known according to the prior art, the crest line remains unchanged and can thus not accelerate the drilling progress.